The invention relates to catalysts used for the reductive conversion of nitrogen oxides in waste gases.
Processes are known for the reductive conversion of nitrogen oxides in waste gases by a catalyst in the presence of ammonia. These catalysts are an intimate mixture of components of titanium in the form of oxides, a metal oxide, for example, vanadium oxide, optionally with the addition of tin oxide and, for example, silicon oxide (see German AS No. 2,458,888). Such catalysts were developed to be able to treat waste gases containing nitrogen oxide (gases which can also contain sulfur oxides) with retention of a high activity for a long period.
A strong oxidation activity toward ammonia, which at elevated temperatures leads to the formation of nitrogen oxides from ammonia, is also known as being disadvantageous in catalysts which are applied to an inert support. Thus, the removal effectiveness thereof for nitrogen oxides necessarily decreases.